Mulching fenced area

I have a customer who's dog has torn up her yard. The yard is basically complete dirt now. She wants me to mulch an area 60' x 40' using a chipped wood mulch. I know how much to charge but should I take any further steps other than just laying the mulch? She is afraid of massive weeds and grass growing up through the mulch. Should I lay the black paper stuff or just spray the area with weed and grass killer? Will the mulch itself prevent the weeds and grass from coming through? Any ideas or comments will be useful. Thanks.

I believe as long as you lay down the mulch thick enough you should not have to worry about the weeds. Seeing as though it doesn't sound like she wants anything to grow there however, I'd go ahead and do some sort of broadcast killer first though.
Maybe mow the lawn as low as you possibly can with an old mower to help kill it, and then spray it, then pile on the mulch.
If she's willing to pay for it though, maybe some mat could be laid down just to prevent any problems down the road?